Raised-cathode gas discharge indicator having a sputter shield

ABSTRACT

A gas discharge indicating device comprising a plurality of symbol-forming cathode elements disposed intermediate a cathodesupporting substrate and a transparent anode connected to one another in a manner to form a hermetically sealed enclosure for containing an ionizable gas, the cathode elements being supported in spaced relation to both the anode and substrate on pins passing through the latter. An insulating shield is provided on each support pin proximate the substrate preferably in noncontacting relation therewith. Under appropriate conditions of gas pressure and anode-cathode and cathode-substrate spacing, localized glow discharges between the anode and selectively energized cathodes are confined to the regions therebetween, resulting in minimized sputtering from the substrate side of the cathode. This feature in combination with the insulating shields operates to preclude sputtered shorting contacts from developing between the respective support pins in the region of the substrate.

United States Patent Inventor James W. Wheeler Scottsdale, Ariz.

Appl. No. 876,618

Filed Nov. 14, 1969 Patented Nov. 2, 1971 Assignee Sperry Rand Corporation RAISED-CATHODE GAS DISCHARGE INDICATOR Primary Examiner-Raymond F. Hossfeld Attorney-S. C. Yeaton ABSTRACT: A gas discharge indicating device comprising a plurality of symbol-forming cathode elements disposed intermediate a cathode-supporting substrate and a transparent anode connected to one another in a manner to form a hermetically sealed enclosure for containing an ionizable gas, the cathode elements being supported in spaced relation to both the anode and substrate on pins passing through the latter. An insulating shield is provided on each support pin proximate the substrate preferably in noncontacting relation therewith. Under appropriate conditions of gas pressure and anodecathode and cathode-substrate spacing, localized glow discharges between the anode and selectively energized cathodes are confined to the regions therebetween, resulting in minimized sputtering from the substrate side of the cathode, This feature in combination with the insulating shields operates to preclude sputtered shorting contacts from developing between the respective support pins in the region of the substrate RAISED-CATIIODE GAS DISCHARGE INDICATOR HAVING A SPUTTER SHIELD BACKGROUND OF THE INVENTION 1. Field of the invention I This invention relates to symbol indicators of the gas discharge type wherein symbols are represented by localized glow discharges between an anode member and selectively energized cathode elements of a plurality of such elements arranged to form various symbols. More, particularly, the invention relates to means for preventing or at least inhibiting the development of sputter-induced shorting contacts between individual cathode elements.

2. Description of the Prior Art it has been observed heretofore that sputter-induced shorting contacts tend to form between cathode elements most readily along the surface of the cathode substrate in gas discharge indicator devices similar to those shown in the appended figures. Accordingly, a recent innovation in such indicator devices provided for the symbol-forming cathode elements to be spaced from the cathode-supporting substrate so as to permit the inclusion of means for inhibiting the formation of shorting contacts along the surface of the substrate. A prior art gas discharge indicator of this type is disclosed in US. application Ser. No. 742,662, filed July 5, 1968, in the name of James B. Armstrong et al. and assigned to the assignee of the present invention. That application relates to a gas discharge indicator comprising a cathode-supporting substrate overlaid by a transparent anode member to form a hermetically sealed enclosure containing ionizable gas. The cathode elements are supported in spaced relation to both the anode and the cathode-supporting substrate on pins passing through the substrate. Glow discharges representative of the symbols to be presented are produced by energizing appropriate cathode elements. As explained in the Armstrong et al. application, the spacing of the cathode elements relative to both the anode and cathode-supporting substrate minimizes sputtering from the substrate side of the cathodes for a prescribed operating pressure of the ionizable gas in the hermetically sealed enclosure. This feature of reduced sputtering in combination with depressions formed in the interior surface of the substrate in the region of the pins passing therethrough retards the development of sputtered shorting contacts between the individual support pll'lS.

SUMMARY OF THE INVENTION The present invention is also directed to apparatus for reducing the formation of sputter-induced shorting contacts between the respective cathode-supporting pins of a raisedcathode gas discharge indicator, particularly in the depressed region of the substrate around or near the cathode supporting pins. in contradistinction to the aforementioned Armstrong et al. application, an insulating shield, typically a nonconductive washer, is placed on each cathode support proximate the substrate and preferably in nonconducting relation therewith. This configuration provides a means for protecting the depression around the cathode support pins from sputtered products although it will be understood that the shield of the present invention may be usefully employed in arrangements which do not include the depressions.

The rationale for the improvement provided by the structure of the present invention is as follows. Metallic ions dislodged or sputtered from the cathode as a consequence of bombardment by particles of the ionizable gas travel along relatively straight paths until they strike another particle or some internal structural component of the indicator tube whereupon they are redirected along another relatively straight path. By virtue of the insulating washers having a comparatively large diameter relative to that of the support pins and further being mounted thereon in close proximity to the substrate, accessibility of the sputtered ions to the surface regions of the substrate immediately adjacent the individual sup port pins is substantially decreased. Moreover, any ions which succeed in reading these regions are restricted to paths at shallow angles relative to the substrate surface. Under such conditions, the ability of the ions to penetrate into the depressions is significantly diminished.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a simplified exploded view in perspective of a typical embodiment of the invention.

FIG. 2 is a section along line 2-2 of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the FlGS., glass substrate 1 is apertured to receive a number of electrical contacting pins 2 which are hermetically sealed to the substrate. The pins extend beyond both surfaces of the substrate so as to be adapted, at the ends beyond the rear surface of the substrate, for connection to a mating pin receptacle (not shown). individual cathode segments 3 are secured to the other end of the respective pins, for example, by welding, to form a conventional alpha-numeric symbol. The lengths of the individual pins are adjusted so that all of the cathode segments lie in approximately the same plane at substantially the same distance from substrate 1. it should be noted that additional symbols and other configurations can obviously be provided, if desired, simply by modifying the number, shape or position of the cathode segments and their associated contacting pins.

Substrate l, is also provided with an aperture 4 to which gas fill tube 5 is hermetically sealed on the side of the substrate opposite the cathode segments. A mercury ampule 6 is inserted inside tube 5. Further, substrate 1 is equipped with an additional pair of hermetically sealed feed through pins 7 and 8 for establishing electrical contact to the anode member 9 of the gas discharge tube. The anode member comprises a glass substrate on which is deposited a thin film 10 of a transparent conductive material completely covering the interior surface facing substrate 1. Anode member 9 is spaced from substrate 1 by glass spacer plate 11 having a main aperture 12 defining a volume for enclosing and ionizable gas to produce cathode glows when the indicator is completely assembled and energized. Spring contacts 13 and 14 pass through a pair of apertures l5 and 16 to establish electrical contact from pins 7 and 8 to the conducting film surface 10 in the assembled unit. The thickness of the spacer plate 11 is determined by the anodecathode and cathode-substrate spacings required to cause only the anode side of the cathode elements to glow under a given gas pressure, taking into account, of course, the thickness of the cathode elements themselves.

in the illustrated embodiment, the spacer thickness is typically 0.040 inch and the cathode segments are spaced from the interior surface 17 of substrate 1 by approximately 0.005 inch. The spacing of the cathode segments from the cathodesupporting substrate can be obtained as explained in the aforementioned Armstrong et al. application by first inserting the pins 2 through substrate 1 so that the ends to be attached to the cathode segments lie flush with the interior surface of the substrate, then hermetically sealing the pins to the substrate and finally etching the interior surface of the substrate to the desired depth. The process is so controlled that a depression 19 is formed in the substrate surrounding the pins. A suitable etchant is a solution of distilled water and hydrofluoric acid. Alternatively, the cathode segments can be spaced from the substrate by adjusting the cathode-supporting lengths thereabove by any conventional mechanical technique. After the cathode-supporting ends of the pins have been elevated above the interior surface of the substrate, insulating washers 18 are slid over the pins and maintained thereon a short distance above the substrate, typically 0.001 inch to 0.003 inch in the illustrated embodiment as by gluing or by means of an abutment or shoulder on the pins. Any material suitable for use in the ionizable gas, such as glass, ceramic, mica or ceramic insulated metals, can be used for the washers. The washer thickness is'not critical. Satisfactory operation has been obtained with washers having a thickness in the range of 0.001 to 0.006 inch, but there is no apparent reason why thicknesses outside of this range would not also be suitable. The washer diameter, however, must be suitable to isolate the desired area around each pin in a manner to achieve the aforedescribed mode of operation. A washer having a diameter of 0.060 inch, for example, has been found appropriate for use with a pin having a diameter of 0.020 inch. in addition the washers should preferably have a diameter such that the difference between the washer diameter and pin diameter is at least twice as great as the separation between the support substrate and the cathode elements.

The indicator is assembled by bringing elements 1, 9 and 1 1 into aligned contact with each other and hermetically sealing the entire edge surface of the aligned unit. Conventional techniques are applied for purging the atmosphere within the sealed unit and then filling and sealing the unit with an appropriate ionizable gasand the mercury contained in ampule 6. The mercury is released into the sealed gas atmosphere at a suitable time during fabrication as is well known in the art to provide therein an amount of this vapor to inhibit cathode sputtering by absorbing a significant amount of kinetic energy of the ionized gas particles before they bombard the cathode segments. I

As hereinbefore explained, construction of a gas discharge indicator in the described manner will essentially eliminate sputtering from the substrate side of the cathode segments, Moreover, sputtered material emanating from the anode side thereof will be effectively blocked by the washers to preclude the formation of shorting contacts between the individual support pins along the interior surface of substrate 1 thereby significantly lengthening the operational life of the indicator. Sputtered material may tend to collect on the upper surface 20 of the washer but electrical contact with the substrate will not be likely since differential temperature expansion and vibration of the various components will prevent the establishment of any permanent low-resistance connection therebetween.

While the invention has been described in its preferred embodiment, it is to be understood that the words which have been used are words of description rather than limitation and that changes may be made without departing from the true scope and spirit of the invention in its broader aspects.

1 claim:

1. A gas discharge indicator comprising a hermetically sealed envelope containing an ionizable gas at glow discharge pressure, said envelope being formed at least in part by a cathode-supporting substrate,

a plurality of electrical-contacting cathode support pins passing through and hermetically sealed to the substrate such that one end of each of the pins extends beyond the interior surface of the substrate, the opposite end of each of the pins being adapted for connection to a source of electrical excitation for selectively energizing the respective pins,

a'plurality of cathode segments attached to the pin ends internal to the envelope whereby said segments are spaced from the interior surface of said substrate, and the segments being arranged so as to provide for the presentation of desired symbols,

anode means supported in spaced relation with respect to said cathode segments,

a depression formed in the interior surface of said substrate around each of the support pins for inhibiting deposition of cathode sputter material on said substrate in the region of each pin, and

an insulating washer member concentrically mounted on each support pin in closely spaced noncontacting relation with the interior surface of the substrate for further inhibiting deposition of sputter material adjacent each pin.

2. The apparatus of claim 1 wherein the insulating washer members have a diameter greater than the diameter of said depressions for acting in combination therewith to inhibit sputter material deposition ad'acent each support pin.

3. The apparatus of claim wherein the insulating washer members have a diameter such that the difference between the insulating member diameter and the pin diameter is at least a factor of two greater than the cathode-to-substrate spacing.

l II 

1. A gas discharge indicator comprising a hermetically sealed envelope containing an ionizable gas at glow discharge pressure, said envelope being formed at least in part by a cathodesupporting substrate, a plurality of electrical-contacting cathode support pins passing through and hermetically sealed to the substrate such that one end of each of the pins extends beyond the interior surface of the substrate, the opposite end of each of the pins being adapted for connection to a source of electrical excitation for selectively energizing the respective pins, a plurality of cathode segments attached to the pin ends internal to the envelope whereby said segments are spaced from the interior surface of said substrate, and the segments being arranged so as to provide for the presentation of desired symbols, anode means supported in spaced relation with respect to said cathode segments, a depression formed in the interior surface of said substrate around each of the support pins for inhibiting deposition of cathode sputter material on said substrate in the region of each pin, and an insulating washer member concentrically mounted on each support pin in closely spaced noncontacting relation with the interior surface of the substrate for further inhibiting deposition of sputter material adjacent each pin.
 2. The apparatus of claim 1 wherein the insulating washer members have a diameter greater than the diameter of said depressions for acting in combination therewith to inhibit sputter material deposition adjacent each support pin.
 3. The apparatus of claim 2 wherein the insulating washer members have a diameter such that the difference between the insulating member diameter and the pin diameter is at least a factor of two greater than the cathode-to-substrate spacing. 